Envelope for a sodium vapor discharge lamp

ABSTRACT

AN ENVELOPE FOR A SODIUM VAPOR LAMP CONSISTS OF A GLASS RESISTANT TO ATTACK BY SODIUM VAPOR WHICH IS AN ALKALINE EARTH SILICATE IN WHICH AL2O3 IS PRESENT, NAMELY A SMALL RANGE OF COMPOSITIONS IN THE SYSTEM   RO-AL2O-SIO2

United States Patent 3,563,772 ENVELOPE FOR A 50911911}? VAPOR DISCHARGE US. Cl. 106-52 Claims ABSTRACT OF THE DISCLOSURE An envelope for a sodium vapor lamp consists of a glass resistant to attack by sodium vapor which is an alkaline earth silicate in which A1 0 is present, namely a small range of compositions in the system Borate glasses which are resistant to the action of alkali vapour and are particularly used as an envelope for a sodium vapour discharge lamp have been known for a long time. Most of these types of glass are not very resistant to atmospheric attack with the result that they require a substrate glass on the inner side of which they are used. The manufacture of such an envelope therefore requires highly qualified professional skill. A plurality of these known glasses devitrify rather easily. In addition most of them have a low softening point and show a resistance to the action of alkali vapour only to a rather low temperature, that is to say, to, for example 350 C.

It is also generally known from experience that the presence of SiO in borate glasses for the above-mentioned use is prohibitive because as a result thereof an intensive brown or black discolouration occurs already at very short contact with alkali vapour.

A class of boro-silicate glasses which do not discolour upon the above mentioned contact is, however, also known, and in connection therewith these glasses were suggested as envelope materials for a sodium vapour discharge lamp. They have a higher softening point than the average borate glasses and are resistant to the action of sodium vapour to a slightly higher temperature. These glasses are, however, not interesting for practical use because their chemical resistance is insufiicient and hence the glass would have to be used again in combinatoin with a substrate glass.

The invention provides a class of glasses which are resistant to the action of sodium vapour to approximately 600, are chemically sufficiently resistant to be used as a self-supporting construction and which can readily be melted in a flame of natural gas without devitrification occurring.

The invention is based on the discovery that silicate glasses do not show discolouration if the SiO.; tetrahedrons are not linked by bridge oxygen atoms but are isolated in the glass network. It was found that this is the case with a group of alkaline earth silicates in which also A1 0 is 3,563,772 Patented Feb. 16, 1971 ice present, namely a small range of compositions in the system of RO-Al O SiO which is situated near the composition gehlenite (2CaO.Al O .SiO

According to the invention the glass which contains SiO A1 0 and alkaline earth oxide is characterized in that it has a composition in mol. percent between the following limits:

SiO 14-43 B 0 0-10 A1 0 9-37 CaO 15-61 BaO 0-35 BeO 0-24 MgO 0-24 Li O+Na O in which the total of CaO-I-BaO -i-BeO+MgO+Li O+Na O amounts 38-36.

In this range of glasses there are those which have to be melted at rather high temperature in order to obtain a product which does not devitrify. For practical considerations those glasses are preferred which can be melted at a temperature between 1500 C. and 1600 C. without any crystallization occurring during cooling. The preferred range of compositions within which the glasses meet this requirement is the following:

sio 27.5-40 B203 0-10 1 8, 10-30 a 154s BaO 15-30 MgO 0-24 BeO o 24 Na O 0 1s Li O+Na O 0 17.5

in which the total of amounts to 42-525.

Slightly coloured glasses are also within this preferred range of compositions so that they are, however, still excellently usable. Only colourless glasses are in the following further preferred range of compositions in mol. percent.

SiO 27.5-40 B 0 O-lO 2 8" 12 33 a BaO 15-24 MgO 0-24 BeO 0-24 Na O 0-15 Li O+Na O 0-17.5

in which the total of CaO-l-BaO+BeO+MgO+Li O+Na O amounts to 42-525.

The processability of the glasses can further be imconsisting of a glass consisting essentially of a composiproved and the risk of crystallisation further be suppressed tion in mol. percent between the following limits: if the content of B is chosen as indicated in the fol- Sio 1443 Wing range 13,0 I:II:III:IIIIIIIIIIIIII: 040

Al O 9-37 sio 275-40 5 1M1 2 3 o 35 2 3 1540 0 0.24 C30 1 o 0 24 B210 15- 10 n fl Mgo T412O-!-Na2O 0 o 24 in which the total of z CaO+BaO+BeO+MgO+Li O+Na o Li O+Na O 0-17.s 2 2 amounts to 38-61.

2. An envelope as claimed in claim 1, wherein the glass ain The glasses accordmg to the mventlon have a Str has a comp0s1t1on 1n mol. percent between the following point of approximately 800 C. which is the temperature at which the viscosity is 1 poises. hunts:

The following glasses mentioned by way of example S10 27.5-40 were prepared by melting a mixture of quartz sand, B 0 0-10 aluminium oxide and calcium carbonate, and if desired A1 0 10-30 barium carbonate, strontium carbonate, lithium carbonate, 15-35 beryllium carbonate and boric acid at a temperature of 1530 approximately between 1690 C. and 1800 C. and 1400 0-24 C. and 1600" C. respectively. The composition of the 0-24 glasses obtained after cooling are shown in the following Na O 0 15 Tables I, II and III, respectively. Li O+Na O 0 17,5

TABLE I Composition, molecular percent Composition in percent by weight S102 A1203 CaO BaO MgO Li O N320 S10 A1203 CaO BaO MgO LizO Nag Nunllb er:

TABLE II Composition in molecular percent Composition in percent by weight SiOg A1203 CaO BaO MgO L120 NazO S102 A1 0; 0110 BaO MgO Li20 NazO Colour Number:

16 33. 3 16. 7 33. 3 24. 6 20. 9 23. 0 31. 5 Light brown.

38. 3 16.7 22. 4 19. 1 l5. 7 42. 8 Do, 37 13 25 25. 3 15. 1 16. 0 43. 6 D0, 20 22 5 23. 8 23. 1 14. 2 38. 9 colourless, 38 16 2d 26. 2 18. 7 14. 8 40. 3 a. Do, 3O 25 22 5 19. 9 28. 2 13. 8 38. 1 Do, 35 20 17. 5 25. 9 25. 2 12. 1 33. 1 D0, 35 2O 2O 24. 3 23. 7 12. 9 35. 5 D 35 20 17.5 24.9 24.2 11.7 31.8 Do

33.3 16. 7 16. 6 25.4 21.7 11.9 32. 5 .e.... DO. d5 20 11.7 24.2 23.6 7.5 41.2 3.5 Light brown,

TABLE III Composition in molecular percent Composition in percent by weight Number: S102 A120; CaO SrO BaO LigO B B20 8101 Alz03 CaO SrO B210 LizO BeO B20 Colour 40. 5 26. 7 4. 8 4. O Light yellow brown. 27. 8 7. 6 8. 3 20. 9 4. 1 27. 7 10. 7 19. 8 24. 9 3.8 Light green. 25. l 8. 0 12. 8 23. G .3. 7 2. 2 Light yellow green. 25.0 12.0 32.7 3. 7 6. 4 Very light yellow.

Outside the range according to the invention there are in whi h th t t l f no sodium resistant compositions which are obtainable in a vitreous state. CaO-l-BaO-i-BeO MgO+Li O+Na O What is claimed is: 1. An envelope for a sodium vapour discharge lamp, amounts to 42-525.

3. An envelope as claimed in claim 2, wherein the glass has a composition in mol. percent between the following limits:

amounts to 42-525.

4. An envelope as claimed in claim 2, wherein the glass has a composition in 1110]. percent between the following limits:

SiO 27.5-40 A1 -30 CaO 15-24 BaO 15-24 MgO 0-24 Na O 0-15 1-Na O in which the total of amounts to 42-525.

5. An envelope as claimed in claim 3, wherein the glass has a composition in mol. percent between the following limits:

SiO 27.5- B 0 1-5 A1 0 15-30 CaO 15-24 BeO O-24 MgO 0-24 Na O 0-15 Li O+Na O 0-17.5

in which the total of CaO-I-BaO-i-BeO+MgO+Li O+Na O amounts to 42-5 2.5

References Cited UNITED STATES PATENTS 2,934,667 4/1960 Pincus 10654X 3,134,920 5/1964 Van De Weijer et a1. 10654X 3,173,779 3/1965 Navias 10654X 3,338,694 8/1967 Davy 106-47UX OTHER REFERENCES Imaoka: Advances in Glass Technology, Plenum Press, New York (1962), p. 154, Glass-Formation Range and Glass Structure.

HELEN M. MCCARTHY, Primary Examiner US. Cl. X.R.

@3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patenr No. 3,563,772 Dated February 16, 1971 (5) HENDRIK J.M. JOORMANN and GUSTAAF A. WESSELINK It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 49, change "combinatoin" to combina Column 2, line 20, change "38-36" to -386l--;

SIGNED AND SEALED THIS 13th DAY OF {1 1; 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

